Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2505.09931

Observation of quantum entanglement in $Λ\barΛ$ pair production via electron-positron annihilation

Junle Pei, X. Q. Hao, Wang, Xiaochuan, Tianjun Li

Published May 15, 2025• 0 citations
arXivHTMLPDF

Abstract

We report the observation of quantum entanglement in $Λ\barΛ$ pairs produced via electron-positron annihilation, specifically through the decay $J/ψ\to Λ\barΛ$. By analyzing the angular correlations of the subsequent weak decays $Λ\to pπ^-$ and $\barΛ \to \bar{p}π^+$, we derive normalized observables $\mathcal{O}_i~(i=0,1,\ldots,4)$ that distinguish entangled states from separable ones. Theoretical predictions for these observables are established, with violations of separable-state bounds serving as unambiguous signatures of entanglement. Experimental measurements at $\cosθ_Λ= 0$ yield $\mathcal{O}_{1\text{min}}^{\text{Observed}} = -0.7374\pm 0.0011\pm 0.0016$, significantly exceeding the classical limit of $-0.5$ with a statistical significance of 124.9$σ$. For $\left|\cosθ_Λ\right|<0.4883$, the observed $\mathcal{O}_{1}^{\text{Observed}}$ consistently exhibits $\mathcal{O}_{1}^{\text{Observed}} < -\frac{1}{2}$ with a statistical significance of at least 5$σ$. Since $69.3\%$ of the decay events involving $Λ\to p+π^-$ and $\barΛ\to \bar{p}+π^+$ are spacelike-separated, our results confirming the persistence of quantum entanglement in the $Λ\barΛ$ system provide strong support for the non-locality of quantum mechanics. The findings are consistent with theoretical expectations under decoherence-free conditions, highlighting the potential of hyperon pairs as probes for fundamental quantum phenomena.

DOI
10.48550/arxiv.2505.09931

Related papers

Testing entanglement between free-traveling electron-positron pairs

Leyun Gao, Alim Ruzi, Qite Li +2 more

Quantum entanglement is a cornerstone of quantum mechanics. While the entanglement of confined electron pairs has been established early on, the entanglement of free-traveling electron pairs, particularly at high energies, remains largely unexplored due to the substantial challenges involved in measuring the spins of free-traveling electrons. In this study, we investigate the entanglement and the Bell inequality violation of free-traveling electron-positron pairs generated in a fixed-target experiment. This experimental setup facilitates the creation of a controllable source of entangled electron-positron pairs, where entangled events are produced in specific phase spaces. Based on this source and the prior knowledge of the entangled state, we demonstrate the feasibility of measuring the polarization correlations of the entangled e + e − pairs through their individual secondary scatterings off two separate additional targets.

arXiv:2502.07597•Physical review. D/Physical review. D.•May 21, 2025•3 citations

Decoherence Puzzle in Measurements of Photons Originating from Electron-Positron Annihilation

Sushil K. Sharma, Divya Kumar, Paweł Moskal

The entanglement of photons originating from electron-positron annihilation has not been experimentally proven.owever, the independent experiments performed so far unanimously confirm that the correlation between the linear polarizations of back-to-back photons from electron-positron annihilation is consistent with the assumption that these photons are entangled in the polarization.Yet, unexpectedly, recent experiments differ as regards the correlation of polarization direction of back-to-back photons after the decoherence induced by the scattering of one of these photons on the electron in the scattering material.In one of the experiments, the correlation before and after the decoherence of the photon state is the same, and in the other experiment, the scattering of one photon leads to a significant decrease in this correlation.Here we discuss this puzzle.Decoherent states were ensured provided by forcing one of the annihilation photons to scatter earlier before measuring the polarization correlation based on Compton kinematics.The comparison is made between the experimental setups used for the different measurements, and the results obtained are briefly discussed, highlighting the parameters that are important in performing such measurements.Finally, the main features of the J-PET detector are presented, along with the schemes for performing similar studies, so that the conclusive results can be used as remarks to solve the puzzle in question.Solving the decoherence puzzle will have crucial consequences for basic studies of entanglement, as well as for the proposed application of the photon polarization in positron emission tomography.If the correlation of the polarization of back-to-back photons from the electron-positron annihilation is the same before and after the scattering of these photons, then it will not be useful for the reduction of scatter fraction in positron emission tomography diagnostics.

arXiv:2210.08541•Acta Physica Polonica A•Sep 1, 2022•16 citations

Testing entanglement of annihilation photons

A. Ivashkin, J. N. Abdurashitov, Alexander Baranov +5 more

We present a new experimental study of the quantum entanglement of photon pairs produced in positron-electron annihilation at rest. Each annihilation photon has an energy that is five orders of magnitude higher than the energy of photons in optical experiments. It provides a unique opportunity for controlled Compton pre-scattering of initial photons before the polarization measurements. The experimental setup includes a system of Compton polarimeters to measure the angular correlations of annihilation photons in initial and thus prepared pre-scattered states. For the first time, a direct comparison of the polarization correlations of initial and pre-scattered annihilation photons has been carried out. The angular distributions of scattered in polarimeters photons turned out to be the same for both types of events. Moreover, the correlation function in the Bell's inequality is also the same for both states. We discuss the implications of our results for quantum measurement theory and for the quantum-entangled positron emission tomography.

arXiv:2210.07623•Scientific Reports•May 9, 2023•55 citations

Test of local realism via entangled $$\Lambda \bar{\Lambda }$$ system

M. Ablikim, Mikhail N. Achasov, P. Adlarson +97 more

Abstract The non-locality of quantum correlations is a fundamental feature of quantum theory. The Bell inequality serves as a benchmark for distinguishing between predictions made by quantum theory and local hidden variable theory (LHVT). Recent advancements in photon-entanglement experiments have addressed potential loopholes and have observed significant violations of variants of Bell inequality. However, these violations do not completely disprove LHVT. To further rule out LHVT, experiments involving massive-entangled particles are necessary, in addition to those conducted with massless photons, which interact electromagnetically. In this study, we utilize (10.087±0.044)×109 J/ψ events collected with the BESIII detector at the BEPCII collider. We present the non-local correlation test of spin entanglement using a massive ΛΛbar bipartite system, which is formed and decays through strong and weak interactions, respectively. Through measurements of the angular distribution of p pbar in J/ψ→ γηc and subsequent ηc→Λ(pπ-)Λbar(pbar π+) cascade decays, a significant violation of LHVT predictions is observed in a loophole-free test of a variant of the Bell inequality, which is given by the Clauser-Horne inequality. The exclusion of LHVT is determined to be significant at a level of 5.2σ.

arXiv:2505.14988•Nature Communications•May 28, 2025•8 citations

Manipulating Bell nonlocality and entanglement in polarized electron-positron annihilation

Hong-Wei Zhang, Xu Cao, Tai-Fu Feng

The hyperon-antihyperon pairs produced in electron-positron annihilation as a massive two-qubit quantum system can be used to study the quantum correlations at high energies. This paper is theoretically dedicated to how polarization of lepton beams manipulates the Bell nonlocality and entanglement of hyperon pair systems. The response of the Clauser–Horne–Shimony–Holt parameter, concurrence, and negativity to the polarization degree of the beam is numerically calculated by exploiting the joint spin density matrix of hyperon-antihyperon pairs. Different influences of longitudinal and transverse polarization of beams on entanglement are found and compared. The results provide alternative perspectives for the decay of charmonium to hyperon pairs.

arXiv:2602.10389•Physical review. D/Physical review. D.•May 21, 2026•4 citations

Bypassing spin-analyzing power dependence for quantum entanglement at colliders: a case study of $$ \Lambda \overline{\Lambda} $$

Junle Pei, Tianjun Li, Lina Wu +2 more

A bstract We study, as a concrete case study using the $$ \Lambda \left(\to p{\pi}^{-}\right)\overline{\Lambda}\left(\to \overline{p}{\pi}^{+}\right) $$ Λ → p π − Λ ¯ → p ¯ π + system, whether quantum entanglement in fermion pairs produced at colliders can be certified solely using angular information from final-state decays, while remaining independent of the parity-violating decay parameters α Λ and $$ {\alpha}_{\overline{\Lambda}} $$ α Λ ¯ . Building on a general decomposition of any angular observable in terms of Wigner d-functions, we show that the expectation value must take the form $$ {\mathcal{O}}_0+{\mathcal{O}}_1{\alpha}_{\Lambda}+{\mathcal{O}}_2{\alpha}_{\overline{\Lambda}}+{\mathcal{O}}_3{\alpha}_{\Lambda}{\alpha}_{\overline{\Lambda}} $$ O 0 + O 1 α Λ + O 2 α Λ ¯ + O 3 α Λ α Λ ¯ , with coefficients 𝒪 i ( i = 0 , 1 , 2 , 3) linear in the spin-density matrix elements $$ {\alpha}_{k,j}{\alpha}_{m,n}^{\ast } $$ α k , j α m , n ∗ . We obtain the value ranges of observables over the general and separable spaces of α k,j , and demonstrate a sufficient entanglement condition for pure states, extending it to mixed states by convexity. In constructing an α Λ - and $$ {\alpha}_{\overline{\Lambda}} $$ α Λ ¯ -independent witness from angular observables alone, we find that there are obstacles to probe quantum entanglement via the inequality-type and ratio-type ways. In particular, for the ratio-type criterion 〈 A 〉/〈 B 〉, the presence of zeros of 〈 B 〉 in both the general and separable spaces of $$ {\alpha}_{k,j}\left(k,j=\pm \frac{1}{2}\right) $$ α k , j k j = ± 1 2

arXiv:2510.08031•Journal of High Energy Physics•Jul 2, 2026•1 citation
Observation of quantum entanglement in ΛΛˉΛ\barΛΛΛˉ pair production via electron-positron annihilation
We report the observation of quantum entanglement in ΛΛˉΛ\barΛΛΛˉ pairs produced via electron-positron annihilation, specifically through the decay J/ψ→ΛΛˉJ/ψ\to Λ\barΛJ/ψ→ΛΛˉ. By analyzing the angular correlations of the subsequent weak decays Λ→pπ−Λ\to pπ^-Λ→pπ− and Λˉ→pˉπ+\barΛ \to \bar{p}π^+Λˉ→pˉ​π+, we derive normalized observables Oi (i=0,1,…,4)\mathcal{O}_i~(i=0,1,\ldots,4)Oi​ (i=0,1,…,4) that distinguish entangled states from separable ones. Theoretical predictions for these observables are established, with violations of separable-state bounds serving as unambiguous signatures of entanglement. Experimental measurements at cos⁡θΛ=0\cosθ_Λ= 0cosθΛ​=0 yield O1minObserved=−0.7374±0.0011±0.0016\mathcal{O}_{1\text{min}}^{\text{Observed}} = -0.7374\pm 0.0011\pm 0.0016O1minObserved​=−0.7374±0.0011±0.0016, significantly exceeding the classical limit of −0.5-0.5−0.5 with a statistical significance of 124.9σσσ. For ∣cos⁡θΛ∣<0.4883\left|\cosθ_Λ\right|<0.4883∣cosθΛ​∣<0.4883, the observed O1Observed\mathcal{O}_{1}^{\text{Observed}}O1Observed​ consistently exhibits O1Observed<−12\mathcal{O}_{1}^{\text{Observed}} < -\frac{1}{2}O1Observed​<−21​ with a statistical significance of at least 5σσσ. Since 69.3%69.3\%69.3% of the decay events involving Λ→p+π−Λ\to p+π^-Λ→p+π− and Λˉ→pˉ+π+\barΛ\to \bar{p}+π^+Λˉ→pˉ​+π+ are spacelike-separated, our results confirming the persistence of quantum entanglement in the ΛΛˉΛ\barΛΛΛˉ system provide strong support for the non-locality of quantum mechanics. The findings are consistent with theoretical expectations under decoherence-free conditions, highlighting the potential of hyperon pairs as probes for fundamental quantum phenomena.
Quantum entanglement is a cornerstone of quantum mechanics. While the entanglement of confined electron pairs has been established early on, the entanglement of free-traveling electron pairs, particularly at high energies, remains largely unexplored due to the substantial challenges involved in measuring the spins of free-traveling electrons. In this study, we investigate the entanglement and the Bell inequality violation of free-traveling electron-positron pairs generated in a fixed-target experiment. This experimental setup facilitates the creation of a controllable source of entangled electron-positron pairs, where entangled events are produced in specific phase spaces. Based on this source and the prior knowledge of the entangled state, we demonstrate the feasibility of measuring the polarization correlations of the entangled e + e − pairs through their individual secondary scatterings off two separate additional targets.
The entanglement of photons originating from electron-positron annihilation has not been experimentally proven.owever, the independent experiments performed so far unanimously confirm that the correlation between the linear polarizations of back-to-back photons from electron-positron annihilation is consistent with the assumption that these photons are entangled in the polarization.Yet, unexpectedly, recent experiments differ as regards the correlation of polarization direction of back-to-back photons after the decoherence induced by the scattering of one of these photons on the electron in the scattering material.In one of the experiments, the correlation before and after the decoherence of the photon state is the same, and in the other experiment, the scattering of one photon leads to a significant decrease in this correlation.Here we discuss this puzzle.Decoherent states were ensured provided by forcing one of the annihilation photons to scatter earlier before measuring the polarization correlation based on Compton kinematics.The comparison is made between the experimental setups used for the different measurements, and the results obtained are briefly discussed, highlighting the parameters that are important in performing such measurements.Finally, the main features of the J-PET detector are presented, along with the schemes for performing similar studies, so that the conclusive results can be used as remarks to solve the puzzle in question.Solving the decoherence puzzle will have crucial consequences for basic studies of entanglement, as well as for the proposed application of the photon polarization in positron emission tomography.If the correlation of the polarization of back-to-back photons from the electron-positron annihilation is the same before and after the scattering of these photons, then it will not be useful for the reduction of scatter fraction in positron emission tomography diagnostics.
We present a new experimental study of the quantum entanglement of photon pairs produced in positron-electron annihilation at rest. Each annihilation photon has an energy that is five orders of magnitude higher than the energy of photons in optical experiments. It provides a unique opportunity for controlled Compton pre-scattering of initial photons before the polarization measurements. The experimental setup includes a system of Compton polarimeters to measure the angular correlations of annihilation photons in initial and thus prepared pre-scattered states. For the first time, a direct comparison of the polarization correlations of initial and pre-scattered annihilation photons has been carried out. The angular distributions of scattered in polarimeters photons turned out to be the same for both types of events. Moreover, the correlation function in the Bell's inequality is also the same for both states. We discuss the implications of our results for quantum measurement theory and for the quantum-entangled positron emission tomography.
Test of local realism via entangled ΛΛˉ\Lambda \bar{\Lambda }ΛΛˉ system
Abstract The non-locality of quantum correlations is a fundamental feature of quantum theory. The Bell inequality serves as a benchmark for distinguishing between predictions made by quantum theory and local hidden variable theory (LHVT). Recent advancements in photon-entanglement experiments have addressed potential loopholes and have observed significant violations of variants of Bell inequality. However, these violations do not completely disprove LHVT. To further rule out LHVT, experiments involving massive-entangled particles are necessary, in addition to those conducted with massless photons, which interact electromagnetically. In this study, we utilize (10.087±0.044)×109 J/ψ events collected with the BESIII detector at the BEPCII collider. We present the non-local correlation test of spin entanglement using a massive ΛΛbar bipartite system, which is formed and decays through strong and weak interactions, respectively. Through measurements of the angular distribution of p pbar in J/ψ→ γηc and subsequent ηc→Λ(pπ-)Λbar(pbar π+) cascade decays, a significant violation of LHVT predictions is observed in a loophole-free test of a variant of the Bell inequality, which is given by the Clauser-Horne inequality. The exclusion of LHVT is determined to be significant at a level of 5.2σ.
The hyperon-antihyperon pairs produced in electron-positron annihilation as a massive two-qubit quantum system can be used to study the quantum correlations at high energies. This paper is theoretically dedicated to how polarization of lepton beams manipulates the Bell nonlocality and entanglement of hyperon pair systems. The response of the Clauser–Horne–Shimony–Holt parameter, concurrence, and negativity to the polarization degree of the beam is numerically calculated by exploiting the joint spin density matrix of hyperon-antihyperon pairs. Different influences of longitudinal and transverse polarization of beams on entanglement are found and compared. The results provide alternative perspectives for the decay of charmonium to hyperon pairs.
Bypassing spin-analyzing power dependence for quantum entanglement at colliders: a case study of ΛΛ‾ \Lambda \overline{\Lambda} ΛΛ
A bstract We study, as a concrete case study using the Λ(→pπ−)Λ‾(→p‾π+) \Lambda \left(\to p{\pi}^{-}\right)\overline{\Lambda}\left(\to \overline{p}{\pi}^{+}\right) Λ(→pπ−)Λ(→p​π+) Λ → p π − Λ ¯ → p ¯ π + system, whether quantum entanglement in fermion pairs produced at colliders can be certified solely using angular information from final-state decays, while remaining independent of the parity-violating decay parameters α Λ and αΛ‾ {\alpha}_{\overline{\Lambda}} αΛ​ α Λ ¯ . Building on a general decomposition of any angular observable in terms of Wigner d-functions, we show that the expectation value must take the form O0+O1αΛ+O2αΛ‾+O3αΛαΛ‾ {\mathcal{O}}_0+{\mathcal{O}}_1{\alpha}_{\Lambda}+{\mathcal{O}}_2{\alpha}_{\overline{\Lambda}}+{\mathcal{O}}_3{\alpha}_{\Lambda}{\alpha}_{\overline{\Lambda}} O0​+O1​αΛ​+O2​αΛ​+O3​αΛ​αΛ​ O 0 + O 1 α Λ + O 2 α Λ ¯ + O 3 α Λ α Λ ¯ , with coefficients 𝒪 i ( i = 0 , 1 , 2 , 3) linear in the spin-density matrix elements αk,jαm,n∗ {\alpha}_{k,j}{\alpha}_{m,n}^{\ast } αk,j​αm,n∗​ α k , j α m , n ∗ . We obtain the value ranges of observables over the general and separable spaces of α k,j , and demonstrate a sufficient entanglement condition for pure states, extending it to mixed states by convexity. In constructing an α Λ - and αΛ‾ {\alpha}_{\overline{\Lambda}} αΛ​ α Λ ¯ -independent witness from angular observables alone, we find that there are obstacles to probe quantum entanglement via the inequality-type and ratio-type ways. In particular, for the ratio-type criterion 〈 A 〉/〈 B 〉, the presence of zeros of 〈 B 〉 in both the general and separable spaces of αk,j(k,j=±12) {\alpha}_{k,j}\left(k,j=\pm \frac{1}{2}\right) αk,j​(k,j=±21​) α k , j k j = ± 1 2